1. Field of the Invention
The invention is related to the field of communication systems, and in particular, to a method and system for improved broadband wireless communications using multiple contention channels for upstream communications.
2. Description of the Prior Art
People and businesses are demanding higher bandwidths from their communication providers. Consequently, the communication providers are looking for ways to increase the bandwidth of their systems using broadband technologies. Broadband technologies are generally referred to as systems that deliver a bandwidth at or above 64 kbps. Broadband technologies can communicate over downstream channels and upstream channels. The customer receives data from another device or system over the downstream channels. The customer transmits data to another device or system over the upstream channels.
Broadband Wireline Systems
One example of a broadband technology is Digital Subscriber Line (DSL) service. DSL service can carry both voice signals and data signals at the same time in both directions. DSL service also can carry call information and customer data. DSL service is typically comprised of twisted-pair wires that connect a customer to a central office. The central office comprises a Digital Subscriber Line Access Multiplexer (DSLAM) that provides the DSL service to the customer. Unfortunately, the speed of DSL service is limited by the distance between the customer and the DSLAM. Customers located too far from the DSLAM may not be able to receive high-speed service. Also, there may not be enough customers within a particular area to make it economical to install a DSLAM. The quality of DSL service is also limited by the quality of the copper wire that connects the customer to the DSLAM. Furthermore, DSL service does not work over Digital Loop Carrier (DLC) lines.
Another broadband technology is cable modem service. The cable modem communicates with a device or system over a coaxial cable. The coaxial cable is typically the same coaxial cable used to receive cable television. The cable modem service can be one-way or two-way. In a two-way system, the coaxial cable carries both the upstream channels and the downstream channels. In a one-way system, the cable modem receives data on the downstream channels over the coaxial cable and transmits data on the upstream channels over a phone line. Unfortunately, the cable modem uses up valuable bandwidth on the phone line in the one-way system. Also, the upstream bandwidth is small over a phone line.
Broadband Wireless Systems
Another broadband technology is broadband wireless service. Customers that subscribe to broadband wireless service communicate with a head end. The head end is a system that transmits data to the customer. In a one-way wireless system, a transmitter antenna for the head end broadcasts wireless signals to the customer on the downstream channels. The transmitter antenna is a satellite antenna or a land-based antenna. The customer transmits data to the head end over another medium, such as a phone line or a cable modem, on the upstream channels. One example of a one-way wireless system is a Digital Satellite System (DSS) from DIRECTV®.
A specific type of broadband wireless system communicates over Multichannel Multipoint Distribution Service (MMDS) frequencies and Multipoint Distribution Service (MDS) frequencies. The MMDS frequencies range from 2596 MHz to 2644 MHz. The MDS frequencies range from 2150 MHz to 2162 MHz. In a typical MMDS system, the total bandwidth of the upstream channels, referred to as the upstream bandwidth, is about 6 MHz. Each of the upstream channels has a bandwidth of approximately 200 kHz.
The head end manages the upstream and downstream channels with the customer. The head end also interfaces the customer with communication systems such as the Internet. The head end includes a base antenna comprised of a transmitter antenna and one or more receiver antennas. MMDS requires a line of sight between devices that are communicating. Therefore, the antennas are placed on a high building or a mountain to establish lines of sight with the customers.
The transmitter antenna is omni-directional and broadcasts data from the head end to the customers on the downstream channels. In a two-way wireless system, the receiver antennas are positioned to receive MMDS signals transmitted from customers on the upstream channels. Each receiver antenna is positioned to receive MMDS signals from customers located within a certain area. The areas formed by the antennas are referred to as sectors. The sectors have designated frequency ranges or designated channels.
The head end is comprised of an upstream manager and a downstream manager that control transmissions on the upstream channels and the downstream channels, respectively. One of the upstream channels is a contention channel reserved for signaling, while the remaining upstream channels are bearer channels. The upstream manager uses the contention channel to control communications over the bearer channels.
In the broadband wireless system, a wireless broadband router is located at a customer premises. The wireless broadband router communicates with the upstream manager and the downstream manager to exchange data. The upstream manager generally operates the upstream channels in four states: idle, contention, polling, and dedicated. In the idle state, the upstream channels are idle. In the contention state, the upstream manager generates and transmits control signals over the contention channel.
For the polling and dedicated states, the upstream manager polls numerous wireless broadband routers to allocate use of the bearer channels. Polling is a round robin process to determine access to a bearer channel. The upstream manager maintains a queue of the active wireless broadband routers to determine which wireless broadband router is next to transmit over an upstream channel for a period of time. The upstream manager keeps an inventory of open upstream channels and waiting wireless broadband routers in the queue.
The upstream manager uses a credit to grant a wireless broadband router use of an upstream channel for a limited period of time. A credit is a message that allows usage of an upstream channel for a period of time or for the transfer of a maximum number of transmission units, such as bytes. One example of a credit is information, such as a particular upstream channel or frequency range, a maximum allowed time to transfer data, and a maximum number of bytes the wireless broadband router is allowed to transfer.
There are two kinds of credits: polling and dedicated. Polling credits are credits related to polling of the wireless broadband routers. Polling credits are generally smaller than the dedicated credits. Once the wireless broadband router completes transfer of the packets, the wireless broadband router transmits a DONE message to the upstream manager via the upstream channels. The DONE messages include information such as the number of bytes sent and the number of packets left for the wireless broadband router to transfer. A DONE message is one example of a termination message. The termination message is any signaling, instruction, or message that indicates termination of access for an upstream channel or completion of a transfer of information or data. Once the DONE message is received, the upstream manager then transmits another credit. If the DONE message shows that the wireless broadband router has more than three packets left to transfer and there are available upstream channels, then the upstream manager issues a dedicated credit to the wireless broadband router.
As stated above, the upstream manager and the downstream manager control transmissions over the upstream channels and the downstream channels. The upstream manager separates the upstream channels into a single contention channel and a plurality of bearer channels. The upstream manager receives requests over the contention channel for access to the bearer channels.
With current upstream managers, such as the CMU-2000-14C from Hybrid Networks, Inc., the upstream channels each have a bandwidth of approximately 200 kHz. With a total upstream bandwidth of approximately 6 MHz, the upstream manager controls about 28 upstream channels. One of the 28 upstream channels is the contention channel. The other 27 upstream channels are bearer channels.
Unfortunately, a single contention channel can limit the communication performance over the upstream channels. This can directly affect the overall performance of the broadband wireless system. The single contention channel and the overall bandwidth of the upstream channels also limit the number of bearer channels that can be used. Consequently, a limited number of bearer channels reduces the capacity of the broadband wireless system. This results in a fewer number of users of the broadband wireless service and a reduced amount of revenues received.